Semiconductive nanowire-based biosensors are capable of label-free detection of biological molecules. Nano-FET (field-effect transistor) biosensors exhibiting high sensitivities toward proteins, nucleic acids, and viruses have been demonstrated. Rational device design methodologies, particularly those based on theoretical predictions, were reported. However, few experimental studies have investigated the effect of nanowire diameter, doping density, and number on nano-FET sensitivity. In this study, we devised a fabrication process based on parallel approaches and nanomanipulation-based post-processing for constructing nano-FET biosensor devices with carefully controlled nanowire parameters (diameter, doping density, and number). We experimentally reveal the effect of these nanowire parameters on nano-FET biosensor sensitivity. The experimental findings quantitatively demonstrate that device sensitivity decreases with increasing number of nanowires (4 and 7 nanowire devices exhibited a ∼38 and ∼82% decrease in sensitivity as compared to a single-nanowire device), larger nanowire diameters (sensors with 81–100 and 101–120 nm nanowire diameters exhibited a ∼16 and ∼37% decrease in sensitivity compared to devices with nanowire diameters of 60–80 nm), and higher nanowire doping densities (∼69% decrease in sensitivity due to an increase in nanowire doping density from 1017 to 1019 atoms·cm–3). These results provide insight into the importance of controlling nanowire properties for maximizing sensitivity and minimizing performance variation across devices when designing and manufacturing nano-FET biosensors.

A major difficulty in the fabrication of nanostructure based electronics is the lack of effective processes capable of precisely arranging nanostructures into predefined positions. Top-down approaches introduce increased complexity and a high cost for practical industrial use, while bottom-up approaches are probabilistic in nature and do not provide precise control of nanostructure properties (i.e., number, diameter), which influence device performance.Alternatively, nanomanipulation promises specificity, precision and programmed motion and its automation may facilitate the large-scale fabrication of nanostructure based devices.This study focuses on the development of an automated contact detection algorithm which positions an end-effector in contact with a target surface without the need for additional equipment, devices or sensors. We demonstrate this algorithm as an enabling feature for automated nano-FET biosensor construction with precise control over nanowire parameters thereby reducing device-to-device variability and also potentially allowing us to optimize individual device performance.iii

Nanowire field-effect transistors (nano-FETs) are nanodevices capable of highly sensitive, label-free sensing of molecules. However, significant variations in sensitivity across devices can result from poor control over device parameters, such as nanowire diameter and the number of electrode-bridging nanowires. This paper presents a fabrication approach that uses wafer-scale nanowire contact printing for throughput and uses automated nanomanipulation for precision control of nanowire number and diameter. The process requires only one photolithography mask. Using nanowire contact printing and post-processing (i.e. nanomanipulation inside a scanning electron microscope), we are able to produce devices all with a single-nanowire and similar diameters at a speed of ~1 min/device with a success rate of 95% (n = 500). This technology represents a seamless integration of wafer-scale microfabrication and automated nanorobotic manipulation for producing nano-FET sensors with consistent response across devices.

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